USPTO Patents Application 10090015

(19)

J

(12)

(43) Date of publication:

01.07.1998 Bulletin 1998/27

(21) Application number: 97310192.6

(22) Date of filing: 16.12.1997

EuropSlsches Paterrtamt
European Patent Office
Off ice europSen des brevets (11) EP 0 851 545 A2

EUROPEAN PATENT APPLICATION

(51) Int. CI. 6 : H01S3/06, G02F 1/313

(84) Designated Contracting States:

(72) Inventors:

AT BE CH DE DK ES Fl FR GB GR IE IT Li LU MC

• Fatehi, Mohammad T.

NLPT SE

Middletown, New Jersey 07748 (US)

Designated Extension States:

• Knox, Wayne Harvey

ALLTLVMKRO SI

Rumson, New Jersey 07760 (US)

(30) Priority: 31.12.1996 US 777891

(74) Representative:

(71) Applicant:

Watts, Christopher Malcolm Kelway, Dr. et al

Lucent Technologies (UK) Ltd,

LUCENT TECHNOLOGIES INC.

5 Mornington Road

Murray Hill, New Jersey 07974-0636 (US)

Woodford Green Essex, IG8 0TU (GB)

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(54) Gain switched optical selector

(57) A gain-switched optical selector is realized by
employing an optical rare earth-doped fiber optical
amplifier as the switching element per se. Each of the
optical rare earth-doped optical amplifiers acts as an
ON/OFF switch. Also, the gain-switched optical selector
of this invention is a natural fit into today's optically
amplified optical communication systems. In one
embodiment, this is realized by employing a pump
select circuit in conjunction with a plurality of pumps and
a plurality of corresponding rare earth-doped fiber opti-
cal amplifiers. The particular pump and corresponding

optical amplifier are selected by use of a monitor
arrangement to determine which signal is to be selected
and routed to an output. In another embodiment, a so-
called tuned pump arrangement is employed in conjunc-
tion with a plurality of filters and a corresponding plural-
ity of rare earth-doped fiber optical amplifiers. A pump
tuning arrangement is employed to control the tunable
pump in order to select the appropriate one of a plurality
of optical input signals at any of a plurality of given
wavelengths.

209.

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COMMAND
UNIT

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LU

Primed by Xerox (UK) Business Services
2.16.3/34

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EP0 851 545 A2

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Description
Technical Field

This invention relates to optica! communication ele-
ments and, more specifically, to optical selector
switches.

Background

An electrical Nx1 selector switch is an Nx1 switch-
ing device which routes any one of the N input lines to
the single output port, as shown in FIG. 1. An optical
Nx1 selector switch is the optical analog of the electrical
Nx1 selector switch where the input and output ports
are optical fibers carrying one or more optical communi-
cation signals at different wavelengths. Certain selector
switches may permit selection of more than one input
port and adding (under certain rules) the signals from
the selected ports. This properly is called the collection
capability of the selector switch.

Prior known selectors employed mechanical
switching elements. Such prior arrangements employ-
ing mechanical selectors were limited in selecting only
one line at a time, their speed was slow, and their relia-
bility was less than desirable. One such arrangement is
shown in FIG. 1 where a plurality of incoming optical
lines 100-1 through 100-N which are supplied to the
selector 101 and switching element 103. Switching ele-
ment 103, under control of actuator 102, then would
select one of the optical lines 100 to be supplied to out-
put optical line 104.

A number of electro-mechanical optical selector
switches are presently available. These devices are
based on mechanically moving the input and/or output
fibers or utilizing various reflective or deflective optical
elements to align beams of light out of the input fibers
and routing them to the output fiber. Clearly, these
mechanical switches are slow and, in most cases, do
not permit collection capability, a desirable feature in
communication systems. In some cases the optical loss
associated with these elements is significant.

Solid state wave-guide selector switches based on
lithium niobate (see for example U.S. Patent 5,181,134)
or indium phosphide optical switching devices are also
available which solve the speed problems. The draw-
back involved with these optical switching devices
include polarization dependence and significant optical
losses. The large optical insertion losses connected
with these devices soon become intolerable when such
devices are concatenated.

Summary of the Invention

The problems and limitations of the prior known
mechanical selectors and various solid state optical
selectors are overcome, in one embodiment of the
invention, by employing an optical rare earth-doped

fiber optical amplifier as the switching element per se of
a gain-switched optical selector. Each of the optical rare
earth-doped fiber optical amplifiers acts as an ON/OFF
switch. Also, the gain-switched optical selector of this

5 invention is a natural fit into today's optically amplified
optical communication systems. In one embodiment,
this is realized by employing a pump select circuit in
conjunction with a plurality of pumps and a plurality of
corresponding rare earth-doped fiber optical amplifiers.

w The particular pump and corresponding optical amplifier
are selected by use of a monitor arrangement to deter-
mine which signal is to be selected and routed to an out-
put. In another embodiment, a so-called tuned pump
arrangement is employed in conjunction with a plurality

15 of filters and a corresponding plurality of rare earth-
doped fiber optica! amplifiers. A pump tuning arrange-
ment is employed to control the tunable pump in order to
select the appropriate one of a plurality of optical input
signals at any of a plurality of given wavelengths.

20

Brief Description of Figures

FIG. 1 is a prior art electro-mechanical selector
arrangement;

25 FIG. 2 illustrates one embodiment of the invention
employing so-called switched pumps with rare
earth-doped optical fiber amplifiers;
FIG. 3 shows a tuned-pump arrangement including
rare earth-doped fiber optical amplifiers; and

30 FIG. 4 shows a switched-pump arrangement includ-
ing a plurality of pumps and corresponding rare
earth-doped fiber amplifiers.

Petailed Description

35

FIG. 2 shows, in simplified form, an embodiment of
the invention including optical fiber lines 201 and 202
which supply optical signals at predetermined wave-
lengths or sets of wavelengths to rare earth-doped fiber

40 optical amplifier (herein after "amplifier") 203 and ampli-
fier 204, respectively. The rare earth doped optical fiber
can be, for example, a length of erbium doped fiber cou-
pled to a wavelength selective coupler, for example, a
wavelength division multiplexed coupler, through 'which

45 a pump is coupled thereto. Further note that loss is
equalized by the length of the rare earth-doped fiber
and gain is equalized by the pump power. As shown,
pump 205 is coupled to amplifier 203, and pump 206 is
coupled to amplifier 204. As is known in the art, each of

so pumps 205 and 206 respectively powers amplifiers 203
and 204. Additionally, it is known, the pumping can be
co-directional or counter directional. Indeed, the pump-
ing could also be bi-directional The outputs of the ampli-
fiers 203 and 204 are combined by an optical star-

55 coupler (herein after "coupler") 207, in well-known fash-
ion. The coupler 207, for a two-optical line arrangement,
is known as a 3dB coupler. The primary output of the
coupler 207 is supplied to output optical fiber 211, which

2

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EP 0 851 545 A2

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may be connected to a receiver or to a long distant
transport fiber. The secondary output of coupler 207 is
supplied to an optical to electrical converter (O/E) 208,
which monitors the power level of the selected line and
determines the parameters and ID (identification) tags 5
associated with selected lines (see for example, EP-A-
0782279.

The information from O/E 208 is supplied to pump
selector 209, which then selects either pump 205 or
pump 206, in accordance with desired parameters, ft 10
should be noted, however, that other optical coupling
arrangements known in the art may be equally
employed in place of coupler 207. This will be apparent
to those skilled in the art. It should be noted that the
secondary output from coupler 207 which is supplied to 15
O/E 208 is optional and this embodiment of the inven-
tion may be utilized without it. The output from O/E 208
is supplied to pump select circuit 209, where it is
employed to further refine the pump selection process.
Specifically, in this example, O/E 208 monitors the 20
power level of the selected signal and determines the
parameters and ID tags associated with the selected
line(s) being supplied to coupler 207. Also supplied to
pump select circuit 209 are command and control infor-
mation from command and control unit 210, which is uti- 25
lized with information from other network elements in an
optical system in order to select which of pumps 205 or
206 is to be selected and, accordingly, which of amplifi-
ers 203 or 204 will be supplying an optical signal via
coupler 207 to output optical fiber 211 as an output, ft 30
should be noted, however, that although we have shown
the use of O/E 208, in this example, that other arrange-
ments may be employed to monitor different parameters
in order to select which of pumps 205 and 206 and,
accordingly, which of amplifiers 203 and 204 will be sup- 35
plying the output.

FIG. 3 shows in simplified form another embodi-
ment of the invention for a plurality of optical fiber lines
301-1 through 301 -N and a corresponding plurality of
rare amplifiers 302-1 through 302-N. In this embodi- 40
ment of the invention, only one tunable pump 308 is
employed, which is coupled to each of filters 303-1
through 303- N though optical star coupler (herein after
"coupler") 309. which gives us the technical advantage
of cost savings. The plurality of filters 304-1 through 45
304-N are associated on a one-to-one basis with ampli-
fiers 303-1 through 303-N, respectively. Again, the out-
puts of amplifiers 302-1 through 302-N are supplied to
optical star coupler (herein after "coupler") 304. The pri-
mary output of coupler 304 provides the system output so
and is supplied to output optical fiber 310, which may be
connected to a receiver or to a long distant transport
fiber. The secondary output of coupler 304 is supplied to
a power monitor unit 305, which monitors the power
level of the selected line and determines the parameters 55
and ID (identification) tags associated with selected
lines (see for example, EP-A-0782279. noted above).
The information from O/E 305 is supplied to pump tun-

ing circuit 306, which then selects one of pumps 303-1
through 303-N, in accordance with desired parameters.
It should be noted, however, that other optical coupling
arrangements known in the art may be equally
employed in place of coupler 304. ft should be noted
however, that although we have shown the use of O/E
305, in this example, that other arrangements may be
employed to monitor different parameters in order to
adjust pump tuning circuit 306 and, hence, tunable
pump 308 and, accordingly, which of amplifiers 302-1
through 302-N will be supplying the output. This will be
apparent to those skilled in the art. It should be noted
that this secondary output from coupler 304 which is
supplied to O/E 308 is optional and this embodiment of
the invention may be utilized without it. The output from
O/E 305 is supplied to pump tuning circuit 306, where it
is employed to further refine the pump selection proc-
ess. Specifically, in this example, O/E 305 monitors the
power level of the selected signal and determines the
parameters and ID tags associated with the selected
line(s) being supplied to coupler 304. Also supplied to
pump tuning circuit 306 are command and control infor-
mation from command and control unit 307, which is uti-
lized with information from other network elements in an
optical system in order to select which wavelength is to
be selected and, accordingly, which of amplifiers 302-1
through 302-N will be supplying an optical signal via
coupler 304 to output optical fiber 31 0 as an output. The
output from tunable pump 308 is supplied via coupler
309 to filters 303-1 through 303-N which, in turn, select
the appropriate one of amplifiers 302-1 through 302-N
to supply an output to coupler 304.

FIG. 4 shows in simplified block diagram form,
another embodiment of the invention employing a plu-
rality of optical fiber lines 401-1 through 401 -N and a
corresponding plurality of rare earth doped optical fiber
amplifiers (herein after "amplifiers") 402-1 through 402-
N. In this embodiment of the invention, a corresponding
plurality of pumps 403-1 through 403-N are associated
with amplifiers 402-1 through 402-N, respectively. The
optical outputs from amplifiers 402-1 through 402-N, in
this example, are supplied to an optical star-coupler
(herein after "coupler") 404. It should be noted, how-
ever, that other optical coupling arrangements known in
the art may be equally employed in place of coupler
404. This will be apparent to those skilled in the art. A
primary output of star-coupler 404 is supplied to an out-
put of optical fiber 408, while a secondary output from
coupler 404, in this example, is supplied to optical to
electrical converter (O/E) 405. It should be noted that
this secondary output from coupler 404 is optional and
this embodiment of the invention may be utilized without
it. The output from O/E 405 is supplied to pump select
circuit 406 where it is employed to further refine the
pump selection process. Specifically, in this example,
O/E 405 monitors the power level of the selected signal
and determines the parameters and ID tags associated
with the selected line(s) being supplied to coupler 404.

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EP0851 545A2

6

Also supplied to pump select circuit 406 are command
and control information from command and control unit
407 is utilized with information from other network ele-
ments in an optical system in order to select which of
pumps 403 are to be selected and, accordingly, which of 5
amplifiers 402 will be supplying an optical signal via
coupler 404 to output optical f foer 408 as an output.

Claims

1. An optical selector having a plurality of inputs and
an output comprising:

a plurality of optical amplifiers corresponding to
the plurality of inputs each employed as a
switching element;

a coupling element for coupling an outgoing
optical signals from each of the plurality of opti-
cal amplifiers;

a pump arrangement responsive to a com-
mand signal for controlling ON/OFF states of
each of said plurality of optical amplifiers so
that one or more of the incoming optical signals
is supplied to the output.

2. The optical selector of claim 1 wherein each of the
optical amplifiers comprises an optical rare earth-
doped fiber having a predetermined length and a
corresponding pump responsive to the command
signal for turning the optical amplifier ON/OFF.

or more of the plurality of optical amplifiers.

7. The optical selector of claim 4 wherein the fiber is
doped with erbium.

8. The optical selector of claim 6 wherein the pump
arrangement associated with the rare earth-doped
fiber is arranged to provide co-directional pumping
of the rare earth-doped fiber optical amplifier.

9. Hie optical selector of claim 6 wherein the pump
arrangement associated with the rare earth-doped
fiber is arranged to provide counter directional
pumping of the rare earth-doped fiber optical ampli-
fier.

15

20

25

3. The optical selector of claim 2 wherein the fiber is
doped with erbium.

4. The optical selector of claim 2 wherein the pump 35
arrangement associated with the rare earth-doped
fiber is arranged to provide co-directional pumping
of the rare earth-doped fiber optical amplifier.

5. The optical selector of claim 2 wherein the pump 40
arrangement associated with the rare earth-doped
fiber is arranged to provide counter directional
pumping of the rare earth-doped fiber optical ampli-
fier.

45

6. The optical selector of claim 1 wherein each of the
optical amplifiers comprises an optical rare earth-
doped fiber having a predetermined length and a
corresponding filter, the pump arrangement includ-
ing a tunable pump and a pump tuning circuit and a so
coupler for coupling an output from the tunable
pump to each of the filters corresponding to the plu-
rality of optical amplifiers, the pump tuning circuit
being responsive to command and control signals

for controlling the tunable pump to supply pumping ss
signals for turning ON/OFF one or more of the plu-
rality of optical amplifiers, the filters filtering the
pump signal to effect the turning ON/OFF of the one

4

INPUT PORT ! o IQH

INPUT PORT 2 0

INPUT PORT N

EP 0 851 545 A2

FIG. 1

PRIOR ART

1

101

ELECTRICAL ACTUATING MECHANISM
AND CONTROL ELECTRONICS

OUTPUT
104

5

EP0 851 545 A2

FIG. 3

INPUT
301-1

INPUT
301-2

INPUT
301 -N

302-1

FILTER

303-1
302-2

FILTER 2 k 303-2

OUTPUT
310

M05

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EP0 851 545 A2

FIG. 4

INPUT
401-1

INPUT
401-2

INPUT
401-N

7